In prior art, a liquid crystal device is comprised of a pair of substrates provided with a pair of electrodes on the insides thereof respectively and a pair of oriented films symmetrically provided on the opposed insides of the electrodes.
On the other hand, it is most impotant to have a sufficiently large coersive electric field Ec (threshold field) of liquid crystal, for active device structures of a liquid crystal device in which nonlinear elements are arranged in a matrix or a row. Under application of an electric field lower than the Ec, liquid crystal holds its initial state (transparent for example), but when applied with an electric field equal to or stronger than the Ec the liquid crystal is quickly reversed its state (opaque for example). Although an Ec exists both positive (Ec+) and negative (Ec-), the two are not necessary coincident in absolute value.
Such an Ec is faint in smectic liquid crystal, especially in chiral smectic C liquid crystal, so that the performance of a device using the liquid crystal is largely depend on the field strength and the pulse width of an applied pulsed electric field. Because of this, prior art employs for matrix display the existing method known as "AC bias method". Also in prior art a rewriting with a positive field is done by once applying a negative pulsed field and then applying a positive pulsed field which has the be finely controlled in strength and in time.
The bias method, however, requires a somewhat complicated peripheral circuit. In order to simplify the peripheral circuit, it is very important factor that liquid crystal employed has a steady and certain coercive electric field. In prior art some liquid crystal devices have been made with a rather certain coersive field by compromising the frequency characteristics or other performances.